DEVELOPMENT OF THE POLYZOA. 185 



Certain branching marine forms are provided with organs 

 like birds' heads, situated on a stalk and called avicularia, with 

 a movable jaw-like appendage, which keeps up an incessant 

 snapping. Beside the avicularia, there are, as in Scrupo- 

 cellaria, long bristle-like appendages to the cells, called 

 vibracula. 



There arc no organs of special sense in the Polyzoa, unless 

 the epistome maybe legarded as an organ of sense, and the 

 nervous system consists of a single rounded ganglion (Frede- 

 ricella}, or, as in Plumatella, a double ganglion, situated be- 

 tween the mouth and vent, from which one set of nerves are 

 distributed to the epistome, lophophore, tentacles, and evagi- 

 nable endocyst, and another set to the various parts of the ali- 

 mentary canal. A so-called colonial nervous system is sup- 

 posed to exist in the Polyzoa, as when the ccencecium in some 

 forms is touched all the polypides become alarmed, which 

 indicates that a set of nerves connect the different polypides, 

 though no such nerves have yet been discovered. The 

 fresh-water Polyzoa are not sensitive to light, nor to noises, 

 only to agitation of the water in which they dwell. 



All the Polyzoa are hermaphrodite, the ovary and male 

 glands residing in the same cystid, the testis being situated 

 near the bottom and attached to the funiculus, while the 

 ovary is attached to the walls of the upper part of the cell. 



Allman regards the polypidc and cystid as separate indi- 

 viduals. The singular genus Loxosoma is like the polypide 

 of an ordinary Polyzoan, but does not live in a cell (cystid). 

 On the other hand, we know of no cystids which are with- 

 out a polypide. Remembering that the cystids stand in the 

 same relation to the polypides as the hydroids to the medusae, 

 as Nitsche insists, we may regard the polypides as secondary 

 individuals, produced by budding from the cystids. The 

 large masses of cells forming the moss-animal, which is thus 

 a compound animal, like a coral stock, arises by budding out 

 from a primary cell. The budding process begins in the 

 endocyst, or inner of the double walls of the body of the 

 cystid, according to Nitsche, but according to an earlier 

 Swedish observer, F. A. Sniitt, from certain fat bodies float- 

 ing in the cystid. 



